Data expiry dates not what they say, be careful if topping up prepaid data

I recently decided to top up my data on my prepaid data LTE that I use at home. The terms and conditions clearly say that previously purchased data packages will be used up first. So I decided to buy a 6 month 50 gig once off to top up my existing 1 year 200 gig previous purchase which had only 7 gig left on it. Well guess what. I now cannot use the 7 gig that are left on the older package. Why because packages with shorter lives are used up first and as the new package is valid for 6 months and not one year you have to use this first. It doesnt matter that the expiry date is after the 1 year package. I have tried in vein 3 times to have them change this but no go! You just have to suck it up and loose your old data!! I will never trust the terms and conditions again. Very annoyed. Makes me move over to fibre earlier than I was planning. Guess what won't get a Cell C deal!!